Pressure sensitive adhesive (PSA) laminates include a supporting web or face sheet, a release liner with a silicone release layer and a pressure sensitive adhesive layer in between them. Some processes for forming labels and other adhesive products cut a plurality of stacked PSA laminates with a knife blade referred to as a guillotine. Although the PSA has been dried, during the cutting operation the adhesive may flow when pressure is applied by the guillotine, smearing the adhesive onto the knife blade and along the sides of the laminate stack. This makes the laminates difficult to separate and results in cutting of fewer laminates with the guillotine. Another problem is the formation of balls of adhesive (referred to as glue balls) on the sides of the laminates, which leads to aesthetic and functional problems; for example, the laminate sheets with adhesive on the edge can jam or deposit adhesive in a printing press, paper-feeder or copy machine. Also, the knife blade, press equipment or copy equipment has to be cleaned at shorter intervals than is desirable.
Acrylic polymer-based pressure sensitive adhesives are known to provide good adhesion to a variety of substrates and good outdoor durability. The adhesives are permanent in that once they are applied to a substrate they cannot be removed without damaging the label or the substrate. This makes acrylic pressure sensitive adhesives suitable for shipping labels and the like.
Some attempts have been made to use silicone compounds in adhesive compositions. For example, one disclosure described silicone acrylate polymer in an adhesive composition. Another disclosure described an acrylic latex emulsion mixed with an emulsion of a nonreactive silicone compound in the formation of an adhesive composition. The contents of U.S. Pat. Nos. 5,154,974 and 4,346,189 are incorporated herein by reference.
Despite attempts to use silicone in adhesive compositions, there remains a need for a pressure sensitive adhesive composition for use in laminates having improved guillotinability while achieving good tack and adhesion to substrates that are difficult to adhere to and that can be easily cleaned from the knife blade.